This invention relates generally to hybrid electric vehicles and, more particularly, to electro-mechanical drive trains for hybrid electric vehicles.
Hybrid electric vehicles are vehicles with more than one propulsion power source. Typically, one of the power sources is an electro-mechanical device, e.g., an electric machine or motor, which is teamed with the other power source, e.g., a combustion engine. The electric machine is coupled to the combustion engine to form the vehicle drive train. Common drive train topologies are shown in FIGS. 1 and 2. In FIG. 1, the combustion engine 20 and the electric machine 22 are integrated into one system ahead of the transmission 24. FIG. 2 illustrates a topology were the electric machine 22 is placed between the transmission 24 and the differential 26. In the drive train of FIG. 2, the output power of the engine travels through the transmission before it combines with the electric machine. The combined power arrives at the wheels via the differential 26. In the topologies of FIGS. 1 and 2, the electric machine propulsion power commonly travels to the differential via a u-joint in front of the differential. U-joints introduce a source of undesirable power loss for any power passing therethrough.
In FIGS. 1 and 2, the drive trains are illustrated as rear-wheel drive trains, but are not so limited. Front-wheel drive vehicles also have drive trains that can incorporate the electric machine before or after the transmission, and before a differential.
There is a need for an improved electromechanical drive train for a hybrid electric vehicle that reduces power losses during transfer to a differential.